1. Field of the Invention
The present invention relates to a trolley pole mechanism for use on an electrically-powered vehicle which draws power from a pair of overhead lines by means of two trolley pole contact arms.
2. Description of the Prior Art
Electrically-powered road vehicles, especially public transport vehicles known as trolleybuses, generally draw electrical power from a pair of overhead lines through two trolley poles articulated to the roof of the vehicle and carrying respective contact heads which rub on the overhead lines. The trolley poles pivot in a vertical plane and resilient means urge them upwards into contact with the corresponding overhead line. The trolley poles also pivot around a vertical axis to permit the vehicle to move laterally relative to the vertical plane passing through the center line of the pair of overhead lines. In their stowed position the trolley poles are folded down against the roof of the vehicle, where they are held in position by means of hooks. Such vehicles are generally fitted with an auxiliary source of electrical power in the form of a battery or generator set, to enable them to move and maneuver to a limited extent with the trolley poles stowed. Deploying the trolley poles involves raising them from the lowered or stowed position to a raised position in which the skid at the end of the pole comes into contact with the respective overhead line from below.
The trolley poles are usually deployed manually, with the vehicle at rest. Attached to the poles adjacent the contact head is a cord which is sufficiently long to remain accessible from ground level with the trolley pole in the completely raised position. These are generally attached to winches known as trolley catchers which are activated when the trolley pole is suddenly released, the skid losing contact with the overhead line, to prevent the trolley pole cutting the lines. To deploy the trolley poles manually, an operator disengages each pole from its hook by pulling on the cord, allowing it to rise slowly and guiding it by pulling laterally on the cord, until the head of the pole is engaged beneath the overhead line. The other trolley pole is then deployed in the same way. This process is somewhat lengthy, and requires a certain degree of skill in that it involves positioning the end of the pole to an accuracy of approximately 1 centimeter laterally and a few centimeters vertically so as to engage an overhead line at least 6 meters above the ground, by maneuvering the trolley pole which is some 6 meters long. As the contact heads of the trolley poles are fitted with skids which pivot as they slide along the overhead line, it is often necessary to adjust the angular position of these skids with the trolley poles in the lowered position, so that when the trolley poles are deployed contact is made properly.
An automatic deployment system for trolley poles has been proposed by the German company Dornier. Motors are coupled to the poles where they are mounted on the vehicle to control the up and down motion and the rotary motion about the vertical axis. The rods are fitted with mechanical sensors comprising a retractable ear on the outside of the trolley pole head, extending above the level of the head. The deployment sequence is electronically controlled and involves first raising the trolley pole heads and simultaneously pivoting the poles around the vertical axes so that the heads move to a position approximately 0.5 meters below the overhead lines, extending a relatively large distance to either side of the overhead lines as seen in plan view. This raising sequence has three final positions: median, righthand and lefthand, so that the pair of overhead lines is correctly bracketed whether the vehicle is below the center line of the pair of overhead lines or to its left or right. In a second stage, the trolley pole heads are raised vertically by approximately half the distance separating them from the overhead lines. In a third stage the heads move closer together until the ears come into contact with the respective overhead lines, so as to orient the corresponding skid. In the final stage the heads are raised, the ears sliding over the overhead lines, until each head comes into contact with the respective line, the ears then retracting rearwards to disengage the contact heads.
Using this system, the driver must select a final position for the first stage, including the height of the trolley pole head above ground, according to the position of the vehicle relative to the overhead lines and the height of the lines above the ground. To ensure that the overhead lines are correctly bracketed, the three final positions available must overlap and the maximum distance either side of the vertical plane through the center line of the pair of overhead lines is approximately equal to the width of the vehicle. Also, the trolley poles must be deployed with the vehicle stationary, as the engagement of the ears with the overhead lines is not compatible with vehicle movement. Moreover, the tolerances in respect of the final position of the first stage are too small to ensure that the position selected when initiating deployment will still be suitable in the final stages, as a result of changes of direction in the event that the vehicle is moving during deployment of the trolley poles.